The Effect of Hydroxyethylidene Diphosphonic Acid on the Chemical Mechanical Polishing of Cobalt in H 2 O 2 Based Alkaline Slurries

Cobalt (Co) has caused much interest as an attractive liner material for Cu for the sub-14nm devices. In this paper, the synergetic effect of H 2 O 2 and hydroxyethylidene diphosphonic acid (HEDP) on the Co polishing performance was investigated. The role of HEDP on the Co material removal process in H 2 O 2 based alkaline slurries was intensively investigated by polishing experiments, potentiodynamic measurements, in situ OCP measurements, and the single frequency EIS experiments. The surface chemical composition of Co was studied by X-ray photoelectron spectroscopy (XPS) measurements, and a complexing mechanism was proposed. It was found that the slurries containing 5 wt% SiO 2 , 0.6 wt% H 2 O 2 , and 0.1 wt% HEDP with 300 ppm MBTA at pH 9.5 was a better candidate for Co barrier planarization, with which Cu/Co wafers showed excellent post-polish surfaces and a good RR selectivity. The mean particle size, zeta potential and large particle counts of the desired slurries were obtained with the purpose of evaluating the stability of the slurries. It was observed that the optimized slurry can be stable for at least 7 d.